A whole medical system that was documented in China by the 3rd century B.C. TCM is based on a concept of vital energy, or qi, that is believed to flow throughout the body. TCM proposes that qi regulates a person's spiritual, emotional, mental, and physical balance and is influenced by the opposing forces of yin (negative energy) and yang (positive energy). Disease is proposed to result from the flow of qi being disrupted and yin and yang becoming unbalanced. Among the components of TCM are herbal and nutritional therapy, restorative physical exercises, meditation, acupuncture, and remedial massage.